1. Field of the Invention
The present invention relates to a plasma display device.
2. Discussion of Background
A thin display device such as a liquid crystal display (LCD) device is mounted on mobile devices such as cell-phones, personal digital assistants (PDA), notebook computers, etc. In such a display device, a cover glass plate so-called a front plate or a front filter is disposed on the front side of a display panel, so that a user will watch a display of the display panel through the cover glass plate (e.g. Patent Document 1).
The cover glass plate is disposed mainly for the purpose of improving the aesthetic impression or strength of the display device, or prevention of impact failures. The cover glass plate is, in many cases, a chemically tempered glass plate having a compression stress layer formed at least at a part of the surface layer in order to improve the scratch resistance. As a method for producing a chemically tempered glass, an ion exchange method may, for example, be mentioned.
In the ion exchange method, glass is immersed in a treating liquid to form a compression stress layer at the surface layer of glass by replacing ions having a small ion radius (such as Na ions) contained in the surface layer of glass with ions having a large ion radius (such as K ions).